XML October 24, Unit 6

What is XML? Stands for eXtensible Markup Language It is a markup language, like HTML But, –XML is designed to markup data –HTML is designed to display data –XML is concerned with what data is –HTML is concerned with how data looks Both use tags, attributes, entities, etc.

XML vs. HTML In HTML –Pre-defined tags –Pre-defined attributes XML –Define our own tags –Define our own attributes –Can have anything we want –Must have a root element

General XML Recommended by the W3C Why? –It is designed to easily transfer data from one system to another –Especially across the Internet With XML we can categorize, structure, organize, and display data –We can use XSL (like CSS) to describe how the data should look More on that later

XML Syntax Again, XML looks a lot like HTML –We have tags, attributes, etc. XML documents require a root element –Must “wrap” around the entire document – is an example We have to create all the tags, attributes, etc. that we need

Recipe Example Recipes have two main parts: –Ingredient list –Steps for preparation So what tags do we need? –Root element: –Maybe a title? : –Ingredients List: –Steps to make the recipe: –Way to list individual items:

Pizza Dough Recipe Pizza Dough 3 c flour 1 c warm water 1 package yeast 2 tbs olive oil Mix water and yeast Combine flour, water and yeast mixture, and oil in a bowl until smooth Cover and let rise until doubled, about 1 hour Divide into 2 portions and use as needed

Adding More Structure Could describe the recipe in more detail What about adding a quantity tag? 3 cups flour Could also add a units tag 3 cup flour Flour is a food item, we could also give it a special tag 3 cup flour

Student List Example CMPT165 Student List Mary Washburn Sam Smith Mike Jones Root element: –

Student List Example, Cont. CMPT165 Student List Mary Washburn Sam Smith Mike Jones Root Element: –

Using Structure How much structure? –Better to have too much than too little –We can always ignore tags If we don’t specify the way they should look, they’ll be ignored Programs can be written which also ignore the tags we don’t want to use Structure should be logical –Not logical to have a tag which goes around each letter in our lists M i x …. –We use tags to describe the data Letter is not the data we are interested in Structure can be used to manipulate the data –For example, if we wanted to double the recipe, it would be easy with the highly structured version and a recipe program Some websites use this

XML Schemas XML is not very useful if we have to define a new set of tags for every single document we write Other people have written sets of tags and attributes for many purposes –These sets of XML tags and attributes are called schemas Common XML schema include: –XHTML –SVG –MathML –OpenOffice

XHTML Defined by an XML schema In the schema it has the tags and attributes we’re used to –Rules relating to those tags must contain at least one Browsers use the definition to display web content The schema being used is part of the very first part of your XHTML pages –(big long text no one can remember)

SVG Scalable Vector Graphics XML language Represents vector graphics on the web Created by the W3C You wouldn’t create or edit an SVG image file in a text editor –But! If there is a definition for an image file available, then any browser, or image editing program could open the file –Not all browsers support SVG yet, some have limited support Example in your course pack, page 112 Figure 6.3 of a smiley face created using SVG

MathML Markup language for mathematical expressions Why? –Mathematical expressions aren’t well supported by most programs And if they are, the expressions are meaningless But most writing type programs support HTML –Difficult because a lot of computers don’t have the required fonts to display the expression –Ever try to add an expression in MS Word? Not trivial Not well-supported by browsers –Mozilla supports this (and I assume the Mozilla family of browsers, Firefox and Netscape) Can include mathematical expression in your web page

OpenOffice Free office-suite of products –Word processor, spreadsheet, etc. Sponsored by Sun Microsystems Open source project –Anyone can look at the code and contribute to it Cross-platform –Windows, Mac, and Linux! The file formats for OpenOffice are XML-based –Why does it matter? Programs with access to the definitions for the file format can all open the documents you create! OpenOffice is almost identical to MS Office in terms of user interface –Good, cheap (read free) alternative to purchasing MSWord

Why XML? So it’s used for lots of things, by why bother? –In general, using XML as a file format is both human and computer readable Not like viewing a.doc file in a text editor –Supports Unicode (can contain pretty much anything) –Strict syntax makes it easy to write programs that can read the xml files –Stored as plain text files –Cross-platform –We can validate it! (I know…your favorite, right?)

Questions?